Optimal Voltage Regulation of Distribution Networks With Cascaded Voltage Regulators in the Presence of High PV Penetration

This work proposes a novel zone-based multistage “time-graded” operation of cascaded on-load tap changing transformers, capacitor banks, and step voltage regulators in the presence of large-scale photovoltaic (PV) sources. A multistage Volt-VAr optimization (VVO) algorithm is proposed to regulate the voltage in a medium voltage unbalanced distribution system while trying to relax the tap/switch operations of regulators that are cascaded in series, and minimize the curtailment of PV inverter output. A linearized power system model is formulated and a mixed-integer quadratic programming solver is utilized to solve the subobjective optimization at each stage in near to real time. The multistage coordinated operations are performed successively based on the regulator zones starting from the zone nearest to the substation, to achieve the overall voltage regulation of the system. Simulation studies were performed for various scenarios of PV and load profile variations. A comparison study between the novel multistage VVO and a multiobjective VVO was done to observe the convergence performance. Results show the efficient usage of the conventional voltage regulating devices along with minimal power curtailment from PVs when required.